The present invention relates to a connector with a rotatable locking ring, particularly for a riser used in offshore oil exploration or production.
The invention will be described with special reference to the described application, which is not limitative, although the connector according to the invention is particularly adapted to solve the connection problems in such a riser.
The most frequently used connectors in this field are of the radially gripping type and their major disadvantage is that they develop very high radial stresses and which result in a poor distribution of the vertical load along the periphery of the connector.
Prior art connectors having a rotatable ring include interlocking tubular elements having an axial abutment, a locking ring inserted in a first tubular element to form therewith a bayonet coupling wherein locking lugs of the ring cooperate with corresponding lugs of the first tubular element, and means bearing on the second tubular element for applying through the lugs of said locking ring, an axial prestress urging the tubular elements against each other.
Connectors of this type, for example, disclosed in French Patent Specification Nos. 2,249,280 and 2,322,323, suffer from a number of drawbacks due to the fact, in particular, that the connection of the two tubular elements is achieved with an angular contact interval between the lugs which is, by construction, smaller than 180.degree., about the connector axis. Consequently the distribution of the axial stresses about this axis is not sufficiently uniform.
Moreover, in these prior art connectors any increase in the prestress urging the two tubular elements against each other results in a corresponding reduction of the above-defined contact angular interval.
The first of these drawbacks can be eliminated by constructing a connector with rotatable ring wherein the first tubular element and the locking ring are each have at least two crowns of lugs which are angularly staggered from one crown to the other.
This provides a connector wherein the lugs of the first tubular element and those of the locking ring contact each other over a much greater angular interval than that obtainable with conventional bayonet connectors.
This angular interval may be close to 350.degree. when the first tubular element of the connector and the locking ring are each provided with only two lug rows (this number being by no way limitative), which provides for a perfect distribution of the axial stresses applied to the connector.
French Patent Specification No. 1,301,318 (Guyot) shows such a pipe coupling provided with locking lugs distributed in alternate rows.
A first embodiment of this coupling suffers from the drawback of requiring a succession of axial displacements combined with a succession of rotations to achieve the connection. This requirement is not acceptable for use in the above-described application.
This drawback is reduced, in a second embodiment, by using rows of locking lugs of different thicknesses, the first row (from the coupling end) being crossed over by exerting an axial force between the two tubular elements of the coupling, thus causing a radial deformation of the wall of the coupling sleeve. This second embodiment requires the use of a sleeve of flexible or semi-flexible material which seems to be incompatible with the considered application.